An electronic receiver forms a basic component in mobile cell phones, wireless personal computers (PCs), and wireless devices in general. Typically, a wireless device is tested for acceptable performance before leaving production facilities. Part of the testing of the wireless device may include testing the sensitivity of a receiver of the device. The sensitivity of the receiver may be tested by calculating a packet error rate (PER) for packets received by the receiver at a given power level. For example, a known number of packets at a predetermined power level are transmitted to the receiver and the number of packets correctly received by the receiver is calculated. The PER is the number of packets transmitted less the number of correctly received packets (i.e. the number of packets not correctly received) divided by the number of packets transmitted, usually expressed as a percentage. A passing score, for example, may be a PER of 10% or less. The predetermined power level is typically chosen at a test level higher than the assumed sensitivity of the receiver. For example, if the assumed sensitivity is −75 dBm (decibels relative to one milliwatt, and thus an absolute power level), the chosen test level may be −72 dBm. If the PER of a receiver is 10% or less for received packets transmitted at a power of −72 dBm, the receiver passes; else the receiver fails the test. If the test level was chosen at or very near the assumed sensitivity of the receiver, then a small variation in power level at the receiver, e.g. due to a loose connector, etc., may cause variable and inconsistent pass/fail test results. Thus, the test level is typically chosen at a point adequately higher than the assumed sensitivity to ensure a stable test result.
An alternative to the traditional testing described above is to search for the true or real sensitivity of the receiver. For example, the PER could be determined for a sequence of packets transmitted at one power level, and then a sequence of packets transmitted at another power level, and continuing in this fashion until a break point (e.g. a point of abrupt change) is found in the PER. The sensitivity is usually specified when the PER reaches a predefined level of, for example, 10% which is typically almost the same as the point of abrupt change. The power level at which the PER break point occurs may be chosen as the true sensitivity of the receiver, and, based on the found true sensitivity, pass or fail the receiver. However, determining the true receiver sensitivity may increase testing time as a number of iterations of a sequence of packets may have to be transmitted at varying power levels before finding the PER break point. In this case, the cost of testing for an acceptable receiver may grow as test time increases. Even so, determining the true receiver sensitivity may be very desirable.
For example, by tracking the true receiver sensitivity for receivers under test, the direction of change in sensitivity level from one receiver to a next, as well as the rate of change, may be known. A change in true sensitivity may be correlated to a change in suppliers for a receiver component. A worsening receiver sensitivity, if found and corrected in time, may prevent the return of failed devices for rework. In addition, modern digital receivers, unlike analog predecessors, do not typically degrade in sensitivity gradually. A large change in sensitivity (e.g. from passing a test to failing a test) may occur within 1 dB of received power. Thus, the true sensitivity break point as a function of power may be a very sharp change in a narrow range of power. Without knowing where the true receiver sensitivity is, or in what direction the true receiver sensitivity is changing, when receivers under test begin to fail, the risk is high that many receivers will fail at once during production testing.
In view of the above, improvements are needed to determine in a timely fashion (e.g. so as not to increase the test time significantly) the true receiver sensitivity for a receiver under test.